“Call them the neuron whisperers. Researchers are eavesdropping on conversations going on between brain cells in a dish. Rather than hearing the chatter, they watch neurons that have been genetically modified so that the electrical impulses moving along their branched tendrils cause sparkles of red light (see video). Filming these cells at up to 100,000 frames a second is allowing researchers to analyse their firing in unprecedented detail.

The idea is a reverse form of optogenetics – where neurons are given a gene from bacteria that make a light-sensitive protein, so the cells fire when illuminated. The new approach uses genes that make the neurons do the opposite – glow when they fire. “It’s pretty cool,” says Dimitri Kullmann of University College London. “It’s amazing that you can dispense with electrodes.”“